Informal. thank God it's Friday.
Why Is Friday The 13th Unlucky?Can you honestly say that you've never felt a slight pang of concern when waking up on the morning of Friday the 13th? You're not alone.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Word Origin and History for tgif
also T.G.I.F., by 1946, slang abbreviation of "Thank God (or "goodness"), it's Friday" (end of the work week).
Online Etymology Dictionary, © 2010 Douglas Harper